Multiple-input and multiple-output (MIMO) technologies are used in access points that have multiple antennas to detect wireless signals and aggregate multiple output connections. Multi-user MIMO (MU-MIMO) is a wireless MIMO technique where one device sends different data to multiple other devices at the same time. The success of an MU-MIMO transmission depends on the precoding done at the transmitter and filtering at the receiver which is standardized in IEEE 802.11ac. Linear MIMO receivers and transmitters perform complicated calculations to generate receive and transmit filters for each subcarrier (i.e., different smaller frequency ranges that collectively define a single frequency band) using channel state information and noise variance estimates. Linear filter design falls into two categories—zero-forcing (ZF) and minimum mean-squared error (MMSE)—both of which require inversion of a Hermitian symmetric covariance matrix R obtained by channel matrix products (H′*H) for each subcarrier in an orthogonal frequency-division multiplexing (OFDM) based communication system—e.g., Wi-Fi and LTE.
Current solutions for calculating the transmit and receive filters compute the required filter coefficients by a factorization of R, followed by double back-substitution for desired filter coefficients. Calculating the filters for each of the subcarriers is complicated and requires a substantial amount of time. Generating accurate filter coefficients requires expensive processing systems and can delay communications between network devices.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.